In recent years, demand for liquid crystal panels has sharply grown due to the proliferation of notebook computers and liquid crystal televisions. Semiconductor devices for operating liquid crystal panels have also rapidly grown in demand. Meanwhile, the need for lower costs of liquid crystal panels and semiconductor devices intensifies in order to achieve popularly priced notebook computers and so on. Thus, methods including Tape Carrier Package (TCP) and Chip On Glass (COG) are frequently used, in which semiconductor devices are directly mounted on a mounting substrate by using an anisotropic conductive sheet and so on. In TCP and COG, an important technical challenge is a stable connection between a mounting substrate and an external electrode of a semiconductor device.
FIG. 10 shows a typical arrangement of input/output pads serving as external electrodes on a semiconductor device (semiconductor chip). Input/output pads 23 are disposed on the edge of a semiconductor device 22 that is disposed outside an active area 21 which has a semiconductor element and constitutes a circuit. As enlarged in FIG. 11, the input/output pad 23 comprises at least an electrode pad 2 which is formed on a surface of a semiconductor substrate 1 and is mainly composed of an aluminum alloy and a metal bump 3 which is formed thereon to make connection with an external lead and is made of a material such as Au and Ni. In order to form the metal bump 3 by electrolytic plating and so on, a protective film 4 is formed beforehand so as to cover the edge of the electrode pad 2. A barrier metal layer 5 is formed depending upon a combination of materials of the electrode pad 2 and the metal bump 3. In some arrangements, for more reliable lead connection of TCP, the metal bump 3 is expanded larger than the electrode pad 2 at least in one direction to have a larger connection area (not shown, see Japanese Patent Laid-Open No. 2001-110833).
However, when the protective film 4 is formed thus so as to cover the edge of the electrode pad 2, a step appears between a surface of the protective film 4 and a surface of the electrode pad 2 not being covered with the protective film 4, and a step appears on a surface of the metal bump 3 formed thereon. That is, since the metal bump 3 is formed on the uneven surfaces of the electrode pad 2 and the protective film 4 by electrolytic plating and so on, a convex portion 3a and a concave portion 3b are formed on the metal bump 3. Despite of the occurrence of steps, electrolytic plating is used under present circumstances because other techniques cannot stably form the protrusion of the metal bump 3.
However, when the metal bump 3 is connected onto a mounting substrate via an anisotropic conductive sheet by COG and so on, some portions may not permit the contact of conductive particles in the anisotropic conductive sheet due to the presence of a step. When the conductive particles do not make sufficient contact, a connection resistance of the semiconductor device and the mounting substrate becomes larger than a design value or is varied. For example, one solution is to make conductive particles sufficiently larger than a step. However, a short circuit is more likely to occur on the adjacent metal bump 3 and thus this solution is difficult to use for the semiconductor device of a small pitch.
The present invention is devised to solve the problem and has an object to provide a semiconductor device which can obtain the connection stability of a metal bump for external connection and a method of manufacturing the same.